oop model Base class design : static and non-static data access

Question

I am trying to make a base class ... tiny framework if you will just for practice

So I start with example of child class because it has less code !!

class User extends Base {

    public $id ; 
    public $username ;
    public $email ;
    public $password ;

    function __construct(){
        $this->table_name = 'users';
        $this->set_cols(get_class_vars('User'));
    }

}

$u = new User;
$u->username = 'jason';
$u->email = '[email protected]';
$u->insert();

Here is my Base class

class Base {

  protected $table_name ; 
  protected $table_columns ;

  protected function set_cols($cols){

      unset($cols['table_name']);
      unset($cols['table_columns']);
      $this->table_columns = array_keys($cols);
  }

  public function insert(){

      $colums = $values = array();

      foreach($this->table_columns as $col )
      {
        if(!$this->$col) continue ;
        $values[] = $this->$col ;
        $colums[] = $col ;
      }


      $values =  implode(',' , $values);
      $colums =  implode(',' , $colums);

    echo  $sql = "INSTER INTO ".$this->table_name ."   ($colums)
      VALUES ($values) ";
  }

}

Here is the problem , I want to make filter or get method (basically reading from database) static and then return an array of objects from database data

    class Base{

      static function filter($conditions =array()){


          $query_condition =  $conditions ; // some function to convert array to  sql string 

          $query_result = "SELECT * FROM  ".$this->table_name ." WHERE  $query_condition ";
          $export = array();


          $class = get_called_class();
          foreach($query_result as $q )
          {
              $obj =  new $class;   

              foreach($this->table_columns as $col )
              $obj->$col = $q[$col];

              $export[]  = $obj;

          }

      return $export;
   }
}

$users = User::filter(['username'=>'jason' , 'email'=>'[email protected]']);

Here is the problem , with filter as static function __construct in User class will not get called and table_columns, table_name will be empty

also in the filter method I can't access them anyway because they are not static ... I can make a dummy User object in the filter method and solve this problems but somehow it doesn't feel right

Basically I have a design problem any suggestion is welcomed

Answer 1

The problem is that the static object is not really "created" when you run statically.

If you want the constructor to run, but still in a static sort of way, you need a "singleton". This is where the object is created once and then you can re-use. You can mix this technique in a static and non-static way (as you're actually creating a "global" object that can be shared).

An example is

class Singleton {
    private static $instance;

    public static function getInstance() {
        if (null === static::$instance) {
            self::$instance = new static();
        }
        return self::$instance;
    }
}

$obj = Singleton::getInstance();

Each time this gets the same instance and remembers state from before.

If you want to keep your code base with as few changes as possible, you can create yourself an "initialized" variable statically - you just need to remember to call it in each and every function. While it sounds great, it's even worse than a Singleton as it still remembers state AND you need to remember the init each time. You can, however, use this mixed with static and non-static calls.

class notASingletonHonest {
    private static $initialized = false;
    private static function initialize() {
        if (!self::$initialized) { 
             self::$initialized = true;
             // Run construction stuff...
        }
    }
    public static function functionA() {
        self::$initialize();
        // Do stuff
    }
    public static function functionB() {
        self::$initialize();
        // Do other stuff
    }
}

But read a bit before you settle on a structure. The first is far better than the second, but even then if you do use it, ensure that your singleton classes can genuinely be ran at any time without reliance on previous state.

Because both classes remember state, there are many code purists that warn you not to use singletons. You are essentially creating a global variable that can be manipulated without control from anywhere. (Disclaimer - I use singletons, I use a mixture of any techniques required for the job.)

Google "php Singleton" for a range of opinions and more examples or where/where not to use them.

Answer 2

I agree with a lot of your premises in your code and design. First - User should be a non static class. Second - Base base should have a static function that acts a factory for User objects.

Lets focus on this part of your code inside the filter method

1      $query_result = "SELECT * FROM  ".$this->table_name ." WHERE  $query_condition ";
2      $export = array();
3
4 
5      $class = get_called_class();
6      foreach($query_result as $q )
7      {
8          $obj =  new $class;   
9
10         foreach($this->table_columns as $col )
11         $obj->$col = $q[$col];
12
13         $export[]  = $obj;
14
15      }

The issue is that lines 1 and 10 are trying to use this and you want to know the best way to avoid it.

The first change I would make is to change protected $table_name; to const TABLE_NAME like in this comment in the php docs http://php.net/manual/en/language.oop5.constants.php#104260. If you need table_name to be a changeable variable, that is the sign of bad design. This will allow you change line 1 to:

$class = get_called_class()
$query_result = "SELECT * FROM ". $class::TABLE_NAME . "WHERE $query_condition";

To solve the problem in line 10 - I believe you have two good options.

Option 1 - Constructor:

You can rewrite your constructor to take a 2nd optional parameter that would be an array. Your constructor would then assign all the values of the array. You then rewrite your for loop (lines 6 to 15) to:

foreach($query_result as $q)
{
    $export[] = new $class($q);
} 

And change your constructor to:

function __construct($vals = array()){
    $columns = get_class_vars('User');
    $this->set_cols($columns);
    foreach($columns as $col)
    {
          if (isset($vals[$col])) {
              $this->$col = $vals[$col];
          }
    }
}

Option 2 - Magic __set

This would be similar to making each property public, but instead of direct access to the properties they would first run through a function you have control over.

This solution requires only adding a single function to your Base class and a small change to your current loop

public function __set($prop, $value)
{
     if (property_exists($this, $prop)) {
          $this->$prop = $value;
     }
}

and then change line 10-11 above to:

foreach($q as $col => $val) {
    $obj->$col = $val
}

Answer 3

Generally it is a good idea to seperate the logic of storing and retrieving the data and the structure of the data itself in two seperate classes. A 'Repository' and a 'Model'. This makes your code cleaner, and also fixes this issue.

Of course you can implement this structure in many ways, but something like this would be a great starting point:

class Repository{
    private $modelClass;

    public function __construct($modelClass)
    {
        $this->modelClass = $modelClass;
    }

    public function get($id)
    {
        // Retrieve entity by ID
        $modelClass = $this->modelClass;
        return new $$modelClass();
    }

    public function save(ModelInterface $model)
    {
        $data = $model->getData();
        // Persist data to the database;
    }
}


interface ModelInterface
{
    public function getData();
}


class User implements ModelInterface;
{
    public int $userId;
    public string $userName;

    public function getData()
    {
        return [
            "userId" => $userId,
            "userName" => $userName
        ];
    }
}

$userRepository = new Repository('User');
$user = $userRepository->get(2);

echo $user->userName; // Prints out the username

Good luck!

Answer 4

I don't think there is anything inherently wrong with your approach. That said, this is the way I would do it:

final class User extends Base {

    public $id ;
    public $username ;
    public $email ;
    public $password ;

    protected static $_table_name = 'users';
    protected static $_table_columns;

    public static function getTableColumns(){
        if( !self::$_table_columns ){
            //cache this on the first call
            self::$_table_columns = self::_set_cols( get_class_vars('User') );
        }
        return self::$_table_columns;
    }

    public static function getTableName(){
        return self::$_table_name;
    }

    protected static function _set_cols($cols){
        unset($cols['_table_name']);
        unset($cols['_table_columns']);
        return array_keys($cols);
    }

}

$u = new User;
$u->username = 'jason';
$u->email = '[email protected]';
$u->insert();

And then the base class, we can use Late Static Binding here static instead of self.

abstract class Base {

    abstract static function getTableName();

    abstract static function getTableColumns();

    public function insert(){

        $colums = $values = array();

        foreach( static::getTableColumns() as $col ){

            if(!$this->$col) continue ;

            $values[] = $this->$col ;
            $colums[] = $col ;
        }

        $values =  implode(',' , $values);
        $colums =  implode(',' , $colums);

        echo  $sql = "INSERT INTO ". static::getTableName() ." ($colums)    VALUES ($values) ";

    }

    static function filter($conditions =array()){


        $query_condition =  $conditions ; // some function to convert array to  sql string

        $query_result = "SELECT * FROM  ".static::getTableName() ." WHERE  $query_condition ";
        $export = array();

        $columns = static::getTableColumns(); //no need to call this in the loop


        $class = get_called_class();
        foreach($query_result as $q ){
            $obj =  new $class;

            foreach( $columns as $col ){
                $obj->$col = $q[$col];
            }

            $export[]  = $obj;

        }

        return $export;
    }

}

Now on the surface this seems trivial but consider this:

class User extends Base {

    public $id ; 
    public $username ;
    public $email ;
    public $password ;

    final public static function getTableName(){
        return 'users';
    }

    final public static function getTableColumns(){
        return [
            'id',
            'username',
            'email',
            'password'
        ];
    }

}

Here we have a completely different implementation of those methods from the first Users class. So what we have done is force implementation of these values in the child classes where it belongs.

Also, by using methods instead of properties we have a place to put custom logic for those values. This can be as simple as returning an array or getting the defined properties and filtering a few of them out. We can also access them outside of the class ( proper like ) if we need them for some other reason.

So overall you weren't that far off, you just needed to use static Late Static Binding, and methods instead of properties.

http://php.net/manual/en/language.oop5.late-static-bindings.php

-Notes-

• you also spelled Insert wrong INSTER.
• I also put _ in front of protected / private stuff, just something I like to do.
• final is optional but you may want to use static instead of self if you intend to extend the child class further.
• the filter method, needs some work yet as you have some array to string conversion there and what not.